Dry etching is a well established technology used in the manufacture of silicon-based semiconductor devices. It is also widely used in the manufacture of non silicon-based products (e.g., GaAs, InP materials) and non semiconductor products (e.g., micro-electro-mechanical-systems (MEMS) devices, hard drive head components, photomasks). All of these applications have a common requirement that a material is etched from a substrate, usually in a pattern defined by a mask such as photoresist or other non erodeable material. In some cases, the substrate itself is etched. To ensure that devices or features located at different locations within the substrate have the same characteristics, it is important that the etch is uniform over the whole area of the substrate. The level of etch uniformity required depends upon the specific application, but it is a general trend that as devices become more complex, the uniformity requirements become more stringent. Thus, although etch uniformities of 5% have previously been acceptable, there is becoming a need for uniformities of 1% or better.
An example is found in the manufacture of Alternating Aperture Phase Shift Masks (AAPSM) where it is necessary to etch a specific depth into a quartz photomask. This etch is required to create a 180° phase shift which, for the 65 nm lithography node, must be accurate to +/−1° of phase angle. This requires that the etched depth is uniform over the whole mask area to approx +/−0.5% (1% range).
High density plasma sources such as Inductively Coupled Plasma (ICP) have become widely accepted in dry etching. Such sources have the advantage of separate plasma density and ion energy control, and efficient plasma production at low pressure (<10 mT) where diffusion ensures good plasma uniformity.
However, even such sources cannot achieve uniformity at the 1% level. The plasma generation is degraded by minor variations introduced during the source construction, by application of the Radio Frequency (RF) and from interactions with the rest of the reactor. The majority of these variations can generally be divided into two classes, symmetric (e.g., radial) and asymmetric (e.g., side-to-side) variation. For ion driven processes (e.g., the Alternating Phase Shift Masks (AAPSM) quartz etch) these asymmetries result in an etch non-uniformity which is undesirable. A number of groups have proposed solutions to the radial non uniformity observed in inductive reactors. These solutions include inserts that physically displace the plasma (see Hieronymi et al. U.S. Pat. No. 5,391,281 and Johnson et al. U.S. Pat. No. 6,339,206), the use of multiple ICP coils (see Barnes U.S. Pat. No. 6,617,794 for example) and for spiral coils, modifying the axial spacing between the spiral coil and the dielectric plate (see Barnes U.S. Pat. No. 6,617,794 and Hashimoto U.S. Pat. No. 6,096,232).
While the methods described in the prior art improve the symmetric uniformity of the plasma, there is a need for an ICP source which can correct for asymmetric etch uniformity.
A number of groups have attempted to correct asymmetric non-uniformity. Yoshida et al. (U.S. Pat. No. 5,690,781) disclose a spiral coil ICP that is movable in the direction parallel to the main planar surface of the dielectric plate by a motor to control the distribution of the etching rate that is not symmetric about the center of the wafer. Yoshida et al. teach that the optimum location of the coil is when the center of gravity of the coil is matched with the axial center of the chamber. Yoshida et al. do not consider the case of radial coil movements for a helical ICP.
Barnes (U.S. Pat. No. 6,617,794) also discusses adjusting the position of ICP coils relative to the dielectric chamber wall. Barnes teaches axial movement of multiple coils that are located concentrically about the vertical axis of the processing chamber. Barnes does not consider radial coil movements to improve plasma density or etch rate uniformity
Becker et al. (U.S. Pat. No. 6,531,031) disclose positioning a helical ICP coil such that the coil and the dielectric cylinder are not concentric. Becker et al. teach positioning the “hot” ends of a helical coil that is powered at both ends at a maximal distance from the ceramic reactor vessel. In this manner, the coil opposite the powered ends is in contact with the ceramic vessel (i.e., the ceramic reactor vessel is tangent to the coil at the location diametrically opposed to the powered coil ends). Becker et al. do not teach a coil that is adjustable along any radial direction in order to correct for an asymmetric etch non-uniformity.
Hashimoto (U.S. Pat. No. 6,096,232) teaches the use of process feedback to adjust the axial distance of a spiral inductor from a dielectric window. Hashimoto does not consider radial coil adjustments. In addition, Hashimoto does not contemplate the case of helical inductors.
Tanaka et al. (U.S. Pat. No. 6,210,539) disclose moving an ICP coil in the axial direction to improve the uniformity in sputtering systems. Tanaka et al. teach positioning the coil within the reactor chamber, at or below the plane of the substrate, to improve uniformity. Tanaka et al. do not consider adjusting the coil in the radial direction to improve asymmetric etch non-uniformity.
Holmann et al. (U.S. Pat. No. 6,217,718) teach tilting an ICP coil located within the plasma reactor relative to the substrate plane in order to affect asymmetric non-uniformity. Holmann et al. do not disclose tilting an externally located inductor.
Therefore, there is a need for improving the etch uniformity in an ICP plasma reactor having a helical inductor.
Nothing in the prior art provides the benefits attendant with the present invention.
Therefore, it is an object of the present invention to provide an improvement which overcomes the inadequacies of the prior art devices and which is a significant contribution to the advancement of the semiconductor processing art.
Another object of the present invention is to provide an apparatus for etching a substrate comprising: a vacuum chamber; a support member in said vacuum chamber for holding the substrate; an etchant gas supply for providing an etchant gas to said vacuum chamber; an RF power source; a helical inductor disposed around or near a portion of said vacuum chamber, said helical inductor inductively coupling energy to said etchant gas to form a plasma in said vacuum chamber; an exhaust in fluid communication with said vacuum chamber; and a mechanism for varying the position of said helical inductor.
Yet another object of the present invention is to provide an apparatus for etching a substrate comprising: a vacuum chamber; a support member in said vacuum chamber for holding the substrate; an etchant gas supply for providing an etchant gas to said vacuum chamber; an RF power source; a helical inductor disposed around or near a portion of said vacuum chamber, said helical inductor inductively coupling energy to said etchant gas to form a plasma in said vacuum chamber; a sensor for measuring a process attribute; a mechanism for varying the position of said helical inductor; a controller connected to said sensor and said mechanism; and an exhaust in fluid communication with said vacuum chamber.
Still yet another object of the present invention is to provide a method for improving plasma uniformity in a plasma etching process, the method comprising: placing a substrate in a vacuum chamber; subjecting the substrate to an inductively coupled plasma etch process within said vacuum chamber; adjusting the position of a helical inductor; and removing the substrate from the vacuum chamber.
Another object of the present invention is to provide a method for improving plasma uniformity in a plasma etching process, the method comprising: placing a substrate in a vacuum chamber; subjecting the substrate to an inductively coupled plasma etch process within said vacuum chamber; measuring a process attribute; adjusting the position of a helical inductor based on said measuring step; and removing the substrate from the vacuum chamber.
The foregoing has outlined some of the pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.